In recent years, with higher integration and higher performance of semiconductor integrated circuits (LSI), new micro-processing technologies have been developed. Recently, to achieve faster performance of LSI, there is particularly a trend to change wire materials from conventional aluminum (Al) alloys to copper (Cu) or Cu alloys (hereinafter, collectively referred to as Cu) having lower resistance. Since it is difficult to perform micro-processing on Cu by the dry etching method used frequently for forming an Al alloy wire, the so-called damascene method by which embedded wires are formed by depositing a Cu film on a dielectric film where a groove processing is performed and removing a portion of the Cu film that is not embedded in the grooves by the chemical mechanical polishing (CMP) is mainly adopted. Generally as the Cu film, a thin seed layer is formed by the sputter process or the like and then a laminated film of thickness of about several hundred nanometers are formed by electro-plating.
Here, when a multi-layer wire is formed by the damascene method or the like in a semiconductor integrated circuit (LSI), a metal cap film may be selectively formed on a Cu wire in order to prevent diffusion of Cu as a wire material into a low-k film in an upper layer as well as to increase adhesiveness to the low-k film. To achieve higher performance of multi-layer wires, the metal cap technology is expected to become necessary in the future. Major candidates of material of a metal cap film include a CuSiN film that is a compound film of Cu, silicon (Si), and nitrogen (N) or a CuSix film that is a silicide film of Cu (see Japanese Patent Application Laid-Open No. 2008-192739, for example). The CuSiN film or CuSix film has an effect of improving adhesiveness of the interface between a Cu wire and an inter-layer dielectric film of the upper layer and suppressing Cu atom transport in the interface between the Cu wire and inter-layer dielectric film. Accordingly, electro-migration (EM) characteristics are improved. However, if tantalum (Ta), which is generally used as a barrier metal (BM) of Cu wire, is used, the improvement factor of electro-migration characteristics is small to achieve only two to three times improvement in terms of the mean-time-to failure (MTF) compared with a case without the CuSiN film or CuSix film. Therefore, further improvement is needed.